MOD002610 Modelling & Simulation for Operations ManagementAssignment case study for Witness modelling and process improvement.Drive shaft manufactureYou have been employed as a member of a production improvement task force for a DriveShaft Manufacturing Company (DSMC). DSMC has been experiencing a severe backlog insales orders due to antiquated machinery and poor production planning. The Company hasjust received an unprecedented contract to supply 450 drive shafts by the process givenbelow. However, finances at present are tight and only £250,000 can be invested. Some ofthe order can be sub-contracted. Your task is to determine the maximum capacity of thecurrent production line after the investment of the £250,000 hence how many parts must bemade by the sub-contractor. The cost list of potential capital improvements is given on nextpage.The current output of the line averages 180 shafts on the two 38-hour shift system.Process:The drive shaft manufacture starts with a bar of 0.3 metres long that is cut into three parts(blocks). The operations are as follows (one machine at each operation unless statedotherwise):1. The bar arrives based on vendor’s supply schedule in lots of 3, every 30 minutes. The barstock buffer can hold only 10 bars.2. In the Saw machine, the time to cut the bar into 3 blocks is 6 minutes. Blade A isreplaced every 40 operation and blade B every 30 operations. Set-up time is uniformlydistributed between 10 and 15 minutes. Time between failures is NEGEXP with meanof 100, and the repair time follows triangular distribution with min 10, mode 25 andmax 30. An operator is required to run this machine.3. After sawing the blocks go to a Fixed conveyor with index time = 0.25 min, length 20parts.4. Once sawed the blocks must be coated for protection. The Coating machine takes 6 partsper cycle and has a cycle time of 60 minutes. Every 10 cycles, the machine is set-up for 5minutes.5. Once coated, the blocks are placed in a staging buffer of capacity 10 part, adjacent tothe Inspector.6. The Inspector draws from the staging area one block at a time and checks thequality of the block’s coating. The cycle time = 20 min, set-up = 1min per part. Ifthe coating is bad, the Inspector puts the rejected block into a Rework buffer ofcapacity 10. The reject rate is 20%, and rejects are returned to be recoated.7. Parts are cured on an individual basis on a chain conveyor (Hardener) of capacity 10parts through a furnace, a process on a first in first out basis. Heat-treat time is 60min.8. The hardened parts go for Gear cutting: cycle time 2 minutes + 1 minute load andunload that is manual, 2 machines, tool change every 100 parts for 10 minutes.Breakdowns mean time to failure 5000 minutes NegExp, repair time normal mean 80minutes σ = 10. One operator runs two machines and changes cutter.9. Four parts are Loaded into a special fixture in 4 minutes before entering for grinding; 10fixtures are available in the system and are stored in a Fixture buffer if not used.10. The 4 parts and the fixture are loaded to the Grinders (2 machines): cycle times M/c 1 =35 min, M/c 2 = 40 min; Time between failures is normal distribution with mean = 75min, SD = 15. The repair time is NEGEXP of mean 15 min and is repaired by the Sawoperator.11. Once ground, the fixture is Unloaded in 4 minutes. The fixture returns to the Fixturebuffer and the parts go to two buffers of capacity 10 parts each.12. The parts are then cleaned in the Wash machine, a multi stage machine with 5 stations, 1part per station, cycle time = 15. Time between failures NEGEXP of mean 120 min, therepair follows Erlang distribution with mean = 20 min, K = 3. The machine is set-upevery 100 operations, time 5 min. Set-up and repair are carried out by the Saw operator.13. The Plating process follows and takes 36 parts per cycle, cycle time 36 minutes, bufferson machine 72 parts both before and after process. Due to chemical change on Mondaymorning, 4 hours are lost. An operator is required.14. The parts are then washed with a Wash machine identical to 12.15. The finished parts are Packed in Pack cycle time of 1.25 min. Packed into flat packboxes one drive shaft per box. Boxes arrive in batches of 1000, frequency of deliveries tobe determined by model. One operator required.16. The boxes are finally shipped.ObjectiveIncrease output.Budget £250 000Production time: two 38-hour shifts (total 76 hours) per week, determine an appropriatewarm-up period.Costs:Cost in £BUFFERSPer Part capacity in any Buffer 100SAW:Identical new saw 40,000Cycle time decrease per 10% 5,000Setup decrease per 10% 8,500New operator 32,000Increase time between failures per 10% 5,000Decrease repair time per 20% 7,500BELT CONVEYORConvert belt to roller 10,000New conveyor of either type 20,000Cycle time decrease per 10% 5,000COATING MACHINEIncrease batch capacity per Part 10,000Cycle time decrease per 10% 6,500Doubling number of operations by decreasing setup time 5,000INSPECTORNew inspector and machine 30,000Cycle time decrease per 10% 10,000Setup time decrease per 10% 5,000Decrease rejection rate by 50% 20,000HARDEN PROCESSCut process time by 10 minutes 20,000Increase capacity per part 10,000LOADER/UNLOADERNew loader or unloader 25,000Decrease cycle time per 10% 15,000New fixture 5,000GRINDERNew grinder 80,000Cycle time decrease per 10% 12,500Double time between failures 30,000CLEANERAdditional cleaner 16,500Cycle time decrease per 10% 10,000Note: Please present the process in a pseudo format before building the model inWitness.New GEAR CUTTING50,000New PLATING machine15,000New PACKING line5,000
